Cellular resinous materials and processes of making the same



May 11, 1954 E.B.MCMHLAN ETAL CELLULAR RESINOUS MATERIALS AND PROCESSESOF MAKING THE SAME Filed NOV. 20, 1948 Patented May 11, 1954 UNITEDsTATEsWPATaNT OFFICE CELLULAR RESINOUS MATERIALS AND PROCESSES OF MAKINGTHE SAME Edward B. McMillan, Marblehead, and Arthur R. Olson, Wakefield,Mass. assigncrs to United Shoe Machinery Corporation,

Flemington,

N. J., a corporation of New Jersey Application November 2o, 194s, serialNo. 61,154

15 Claims.

This invention relates to a new cellular resinous material and to a newprocess vfor molding cellular resinous articles.

Plastic articles have been formed in various shapes by molding liquidresins or resin powder under heat and pressure. Because of the necessityof applying pressure, design of molding equipment particularly forcomplex shapes is extremely difcult and the equipment is costly.

Fig. 1 is a partial sectional elevation of a moldA for the heel part ofa last filled with the new molding material according to the presentinvention;

Fig. 2 is a sectional elevation of the mold with the molded materialtherein after treatment to convert the molding material into a hard,strong, cellular material; l

Fig. 3 is a drawing from a photomicrograph of a cut and polished sectionof the cellular material of the present invention and Fig. 4 is anelevation view of the molded heel.

part of the last after removal from the mold ihmold. Where a curing orheat-hardening and trimming of excess material therefrom, and

with a last forepart shown in broken lines assembled with the heelparli.

yIn accordance with'the present invention heat softenable resinousmaterial, preferably of the type which is first softened and then curedor hardened by heat, is compounded with a blowing agent and thecompounded material is divided intoy solid granules. A simple mold-suchas the two part mold shown in Figs. 1 and 2, or any heat resistantcontainer, is filled with the granules, and the granules are then heatedto soften the granules, and to cause the blowing agent to evolve gas.The evolved gas expands the individual solid ygranules to ll theintergranular spaces andto force the faces of the expanded granules intocontinuous contact with the surfaces of adjacent granules and with 'thesurfaces of the resinous material is used, heating will be continued tocure or harden the material. The

molded article may then be removed from theV Y mold.

The product obtained Iby the foregoing method possesses unusual strengthdue to the structure resulting from the expansion and fusing together ofthe resinous granules. At the area of contact between adjacent expandinggranules, the vsurfaces are fused together so that there results (seeFig. 3) a continuous cellular structure shown as thick lines 6 ofsubstantially nonporous resinous material defining enclosed spaces orcells 3 which are filled with expanded resinous material. The non-porouscellular structure apparently contributes strength of the product. Alsothe area of fusedtogether surface between the granules is large andgives a strong integral body which shows no tendency to separate alonglines corresponding to junctures between granules in the initialcomposition. In a preferred form the mold is filled with granules beforeheating and remains filled during and after the heat treatment therebeing substantially no overall volume change in the resinous material.In this form the original distribution of resinous material in themolded article is not disturbed. This form is of particular advantagefor providing a light, strong, permanent filling between spacedsurfaces, for example to ll the hollow interior of metal or otherstructures or to provide a light core which is bonded by its ownadhesive properties to spaced metal or other sheets. v

To obtain the unique advantages of the present invention it is importantthat the resinous material be softened at a temperature below that v atwhich the blowing agent develops substantial blowing pressure to areadily deformable and tacky condition in order that the granules may beshaped under the expansive action of the blowing agent to fill theintergranular spaces and bond with adjacent expanded granules; but

that the material become strong and firm when cooled or after curing. Asa simple criterion of physical properties which should exist in theheat-softened state, it may be stated that it is desirableY that inheat-softened condition thev resinous material be sufficiently soft thatwithto the mechanical l out the generation of gas within the granules bythe blowing agent, the mass of granules will shrink in volume and owtogether. It is likewise important that the resinous material inheat-softened condition form films of sufcient strength so that thebublbles do not rupture to form large void spaces within the blownmaterial.

This combination of physical properties may be secured by mixture of arubber-like material and a heat softenable resin which is strong andrigid in set condition. The need to be heat softenable exists onlyduring the stage of expansion of the individual granules and in theknitting together of the expanded granules duringY the formation of thenew cellular material; and the expression heat softenable resin which isstrong and rigid in set condition includes resins which are heatsoftenable. at thisstage, both those resins which are permanentlythermoplastic and those which are softened by heat in the state in whichthey exist. at this stage, but which become infusible after this heatingstep.

Many resinous compositions may be selected possessing properties makingthem suitable for use to form the new article according to the method ofthe present invention.

A resinous material which has been found particularly satisfactory inthe manufacture ofl articles which must be light and strong, suchaslasts, comprises from 50 to 75 parts of a heathardening phenolic resinand from 50 to 25- parts of a compatible solid plasticizer such as asynthetic rubber, e. g. a butadiene-acrylonitrilecopolymer syntheticrubber. A phenolic resin which has been found useful is Durez resin#12687 obtained' from the Du-rez Plastics 8a Chemicals Co. of NorthTonawanda, New York, which is understood to bea condensation of a eashewnut shell oiland another phenol with an aldeA hyde.. This type of resinis described in greater detail in United States Letters. Patent to`Alvin F. Shepard et al., No. 2,203,206, granted June 4, 1940. Othersuitable phenolic resins include Resins. 378 and L-9718 obtained fromthe Mon-- santo Chemical Co. o-f St. Lou-is, Missouri, and Resin 12315obtained from the General Electric Co. of Schenectady, New York.

Suitable solid plasticizers. for the phenolic. resin includeV copolymerrubbers such as Hycar ORf- 25 and Hycar OR-l5 which are understood tocontain, respectively, 33% and 45% acrylonitrile and which are obtainedfrom the B. F. Goodrich Company, of Akron Ohio. Other cpolymer rubbers,such as Chemigum N3 and N4 which are obtained from Goodyear Tire andRubber Company, of Akron, Ohio, various Butaprenes obtained fromFirestone Tire and Rubber Co. of Akron, Ohio, and Perbunans obtainedfrom Enjay Co. of New York, N. Y., may be used provided they contain atleast 20% acrylonitrile. To obtain the desired plasticizing action ofthe copolymer on the resinous material there may be employed from 30 to100 parts of the copolymer to 100 parts of the resinous material.

Other compatible low-melting plasticizers such as a coumarone-indeneplasticizer (Piccoumaron 422R) which has a melting point of '75 C. orplasticizer Durez 13698 may be added for the usual purposes.

Other resinous compositions which may be employed according to thepresent invention to form the new, light, strong, cellular materialinclude intimate mixtures of from 55 to. 70% of polyvinyl chloride withfrom 45 to 30% of butadiene-acrylonitrile copolymers containing from 25to 45% acrylonitrile, intimate mixtures of resinous high styrene contentcopolymers of styrene and diolefins with a synthetic rubber such aspolychloroprene or rubbery lower styrene con tent copolymers of styreneand butadiene. The high styrene content copolymers may contain from 60to 90% styrene. Other resinous compositions or mixtures possessing theproperties noted above may be employed according to the presentinvention.

With the resinous material there is incorporated suicient blowing agentto maintain the volume of the material and to insure satisfactorymolding pressure. A preferred range is from 3 to 20 parts by weight of ablowing agent to parts by weight of the resinous material. Anyconventional blowing agent may be used but it has been found that theblowing agents Unicel (diazoaminobenzene) obtained from E. Du Pont deNemours andl Company, ammonium bicarbonate or sodium bicarbonate aloneor with stearic acid and blowing agent No, 15, understood to be biuretand urea in equimolal proportions, which is obtained from the SherwinWilliams Company, are particularly satisfactory. It. has been observedthat in compositions including a curing agent such as hexamethylenetetramine which evolves gas during the curing cycle, the conventionalblowing agent may be. employed in reduced proportion o1" even omitted.It isk toI be understood that in the specification and claims, referenceto a blowing agent includes such gas generating agents, even though theyserve to give the additional effect o-f curing.

These blowings agents may be compounded with the resinous material on amill or in a Banbury mixer or in any other mixing equipment. Thetemperature of mixing must be kept below that value at which the blowingagent generates gas, and with the above agents itv has been found thatsatisfactory mixing can be obtained at temperatures of from 14:0 to 20.0F.. The mixture is sheeted out and permitted to cool to a friable massand is then broken up into solid granules of a desired size. For use ina last, granules oi from of an inch to about 1/4 of an inch have beenfound very satisfactory. For other uses the material may be reduced to apowder or may be used in even larger particle. sizes.

The composition comprising the resinous. material and the blowing agentis satisfactory for use in forming tough, strong articles; but forvarious purposes including improving the cold flow characteristicsand/or reducing the cost of the material, there may be employed a fillersuch as lignin or mineral fillers including clay, channel black, calciumcarbonate or other known mineral filler. A quantity of filler upto aweight approximating or even slightly exceeding the total weight oftheresinous material and plasticizer may be employed. The ller will beincorporated in the resinous material by the same procedure and at thesame time as or before incorporation of the blowing agent.

A mold used in forming an article using the material of the presentinvention may comprise a simple two-part mold, shown in Figs. 1 and 2 asa mold for the heel part of a last. The parts 10- and 12 of the moldcomprise shaped surface portions 14 and cooperating flange portions lo'.A funnel shaped opening 18 is provided in the upper portion of the lastmold for filling materital into the mold after assembly of the twoparts. A removable insert bar 22v projects into the mold through a slotin part 10. of the mold.

The inner end of the bar is xed in position by a bolt 24 which extendsthrough holes in the sides of the mold parts and 12 and through a holein the end of the bar 22. The bar 22 and bolt 24 mold a slot and hole inthe heel part for receiving a hinge link and hing-e pin respectively inassembling the heel part with a forepart of a last, as illustrated inFig. 4.

The granules 20 containing a blowing agent are placed in the mold asshown in Fig. 1. The quantity of granules in the mold and hence theultimate density of the molded article will depend on the size of thegranules and the vtightness vvith which they are packed. In general,larger granules tend to pack less tightly. By proper selection of sizeof particle and variation in the quantity of granules in the mold,specific gravities ranging from 0.1 to a value somewhat less than thatof the resinous material have been obtained. For use in making lastparts, specific gravities of from 0.7 to 0.9 have been foundsatisfactory. The filled mold is subjected to heat suiiicient to softenparticles and to cause them to expand under the action of the blowingagent. The expanded particles sinter together into an integral cellularmass which, due to the' action of the blowing agent, is pressed intomolding contact With the surfaces of the mold. The time of heatingrequired will vary depending on the cross section of the mold, thetemperature of heating, the nature of the material of the particles, thecuring agent, and other facto-rs known to the skilled chemist. With theheel part mold of Figs. 1 and 2 a heat treatment of approximately threehours at 135 C. has been found satisfactory to cause expansion andsintering of the granules and curing of material comprising a phenolicresin and a. butadiene acrylonitrile copolymer synthetic rubber. Theexpanded sintered mass (see Fig. 2) is removed from the mold aftercuring and excess material is trimmed off to form the final moldedarticle. In the present case a last heel part 26 is formed which may beused Without further finishing operations in combination with a forepart28, shown in broken lines in Fig. 4. The following examples are given toassist in understanding the invention. It is to be understood that theinvention is not limited to the materials, proportions, or operationaldetails disclosed in the examples.

Example 1 Parts by weight Cashew nut-shell oil-phenol aldehyde resin(Durez resin 12687) 300 Butadiene acrylonitrile copolymer containing 33%acrylonitrile-Hycar 0R25 100 Dixie clay 2.25 Coumarone indene resinhaving a melting v point of 75 C. (Piccoumaron 422R) 20 Diazoaminebenzene (Unicel) 7 The above materials were mixed on a Banbury mixer ata temperature which varied from 140 to 200 F. lIlhe mixture was sheetedout and permitted to cool to a friable condition. The cooled materialwas then broken up to a particle size comprising granules ranging from11g inch to 1A; inch. These granules were then poured into a heatedlubricated mold similar to thatshown in Figs. 1 and 2 at a temperatureof 100 C. in quantity sufficient to completely fil1 the mold. Thetemperature of the mold Was brought to 135 yC. and maintained at thattemperature for three hours. The mold and its con- 6 tents were cooledand the mold removed yfrom. the molded article. The resulting moldedlast heel part conformed faithfully to the shape of the mold and afterminor finishing operations lwas assembled with a last forepart as shownin Fig. 4 to form a last suitable for the lasting of shoes. The moldedmaterial had a specific gravity of 0.80.

Eample 2 Parts by weight Marbon S Darex #3 160 GRS-l0 50 Zno 15.5Stearic acid 31.1

Sulfur 7.9 Piccoumaron 457 47' Piccoumaron 452 47 ANaI-1G03 62 Unicel 47y Santocure 3.9

Marbon S is a copolymer of styrene and selected diolens obtained fromthe Marbon Corporation, Gary, Indiana. Darex #3 is a copolymer ofbutadiene and styrene containing 70% styrene obtained from the Dewey &Almy Chemical Co. of Cambridge, Massachusetts. GRS-10 is a copolymer ofbutadiene and styrene containing 30% styrene. Piccoumaron 457 is acoumaroneindene resin having a melting point, ball and ring of 30 toy 35C.; and Piccoumaron 452 is a coumarone-indene resin having a meltingpoint, ball and ring of 80 to 90 C. These Piccoumaron resins areobtained from the Pennsylvania Industrial Chemical Corp. of Clairton,Pennsylvania. Santocure (N-cyclohexyl-Z-benzothiazole sulfenamide) is acuring agent produced by the Monsanto Corporation of St. Louis,Missouri.V

The above materials were mixed, sheeted out and granulated as inExample 1. The granules were poured into a hot mold similar to thatshown in Figs. 1 and 2 at a temperature of 135 C. and were cured forthree hours at,135 C. The mold was then cooled and the molded materialremoved. The resulting last'heel part conformed faithfully to thecontour of the mold surface and was found to be strong and resistant tofracture under the conditions encountered in its use in making shoes.

Eample 3 c-eon Polyblend 500x329 "gms" 33o Unicel -parts by weight 15Geon Polyblend is a mixture of 45% of Hycar OR and 55% of polyvinylchloride obtained from the B. F. Goodrich Co. of Akron, Ohio.

The above materials were mixed, sheeted out and granulated as in Examplel. The granules were poured into a hot mold at a temperatureof C. forone hour. The mold was then cooled and the molded material removed fromthe mold.

The.. resulting material was light, porous, and` strong.

Example 4 Parts by weight MarbonS Neoprene GN '60 suene so Unicel 8jPiccoumaron 422B. 40 Sulfur 4 Altax 6 Z110 29 4'and granulated asv in''Example 1. 'temperature of 135. C.` waslled with the composition, andthe mold and granules were heated "iPiccoumaro'n 422R, is acoumarone-indenefresin fobtainedvfrom the' Pennsylvania IndustrialChemicalCorpand has a meltingpoint, ball and ring ofi-SOHtQO" C.

" Th-e'above materials were'mixed, sheeted out, A mold at a "Wiseworked-1with-'woodworking machinery.

-Having-described our invention, what we claim as newY and desireto-secure-by Letters Patent 'of the UnitedStates-is:

1. A light,.strong,.integral, continuous, cellular materialcomprisinganetwork of relatively thick substantially nonporous resinousmembranes de- `z1ih1`-ng-cells-and thinnermembranes of the samecomposition asthe network subdividing said-cells into smaller units,said resinousmaterial` comprising an Yintimate `mixture of from 100 to300 parts byweight of a heat-softenable -resinwhich is-st-rong andrigidinsetcondition, and 100 parts byweight of a synthetic polymerrubber.

2.A light, strong, integral, continuous cellular material comprising anetwork of relatively thick substantially nonporous resinous membranesdework subdividing said cells into smaller units,

said resinousvmaterial `comprising the reaction product Vofathermosetting phenol-aldehyd-e resin anda butadiene acrylonitrile.copolymer containingat least acrylonitrile.

4. A light, strong, integral, .continuous cellular material comprising anetwork of relatively thick substantially nonporous resinous membranes.defining cells and thinner membranes-oi the same-composition as thenetwork subdividing said cells into smaller units, said resinousmaterial-comprising the reaction product Vof athermosettingphenol-aldehyde resin and a butadiene acrylonitrile copolymer containing'at least' 20% of acrylonitrile, said copolymer and the phenolaldehyde-resin being present in the ratio of from 100 to 300 parts 'of the resinwith 100 parts of the copolymer.

l"5. Alight, strong,-integral, continuous cellullar material comprisinga network of relatively thick substantially nonporous resinous membranesdefining cells and thinner membranes of substantially the samecomposition as the network subdividing said cells into smaller units,said-v resinous material "comprising polymerized vinyl `chloride 'and'va butadienev acrylonitrile copolymer.

6.1ight, strong, integral, continuous cellulai` material comprising anetworkofrelatively 'thick substantially rnonporous resinous membranesdeningcells and vthinner membranes of tl'iesarner composition Aas'thenetwork subdividirig saidV cel-lszinto smaller: units; saidiresinous ma- Vterial comprising4 an"v intimate mixtureA cia-styrenecopolymer ofhigh' styrene content.: and a copolymer `synthetic rubber.

'7. A light, strong,i integral, continuous'4 cellular. materialcomprising-a network of relatively thick substantially nonporousresinous membranes defining cellsand -thinner kmembranes of V the samecomposition as the networkfsubdividing 'said cells into smaller units,said resinous materialfcomprising ranfintimate mixture of a styrenecopolymer cfr-high styrene content and' a butadiene-styrene fcopolymersynthetic rubber containing 30% styrene. l

8. A process-for forming astrong', light, cellular, integral 'materialwhich comprises ldisposing in a confined space dense ysolidv granulescomprisingu a blowing agentl and an intimatemixture of from td 300 parts4by weight of a heat-softenable resin which :is strong and v'rigidi' inset condition and' 100l parts by weight of a synthetic polymer rubber,said mixture being characterized by iiow properties such Vthat a massofgranules of'themixture freey from a blowing agent would shrink involume and flow together when softened by heat, said blowing agent'being within the individual solid granules, and'heating 'the granules tosoften them and tocause the blowing .agent to evolve gas, whereby theindividual granules are expanded, the surfaces of the expanded granulesare forced into contact with thefsurfaces ofl adjacent granules and thecontacting surfaces are sintered together into acontinuous network ofrelatively thick, substantially nonporous .resinous membranes denningcells; "the expanded resinous material of the interior of the granuleslforming 'thinner membranes` 'subdividing' `said cells "into smallerunits.

9.v A process for forming a'strong, li'ghtycellular,integrali-materialwhich comprises' disposing in a connedfspace dense,solid granules comprising a blowing agent and` an-intimate mixture offrom 100 lto 300 parts by weight'of a heat-softenlablev resin which isstrong and rigid yin set condition and 100 parts by weight 'of' acopolymer `synthetic rubberfsaid mixture `being characterized rbyl owproperties such-that a mass of' granules 'of the mixture free fromblowing agent would shrink in'v'olume 'and'flow 'together ywhen softenedby heat and said blowing agent being-within the individualsolidngranules, and heating the granules .tosoiten them and to cause theblowing agent. to .evolve gas, wherebylthe individualgran- .ules areexpanded and the surfaces -of--theexpanded granules are forced intocontactwiththe surfaces of adjacent granulesand the contacting surfacesare sintered together into a continuous network l.of relatively` thick,Vsubstantially Vnonporous resinous membranesfden-ing cells, the expandedresinous material, of .the interior of the granules forming thinnermembranes subdividing said cells into smaller units.

10. A process for forming a strong, light, cellular, integral materialwhich comprises disposing in a coniined space dense; solid granulescomprising a blowing agent and an intimate mixture of abutadiene-acrylonitriley copolymer containing at leastr20% acrylonitrileanda Vthermosetting phenol' aldehyde resinv reactive therewith, saidmixture being characterized by ow propertiessuch that amass of granulesof the mixture "free from blowing agent "would'shrink in volume and flowtogether'rwhen softened: by;heat; and saidy blowingagentrbeing'rwitlnnAthe' v'individual solid granules, and heating the granules to softenthem and to cause the blowing agent to evolve gas, whereby theindividual granules are expanded and the surfaces of the expandedgranules are forced into contact with the surfaces of adjacent granulesand the contacting surfaces are sintered together into a continuousnetwork of relatively' thick, substantially non-porous resinousmembranes dening cells, the -expanded resinous material of the interiorof the granules forming thinner membranes subdividing said cells intosmaller units, and continuing heating to cure the resin.

11. A process for forming a strong, light, cellular integral materialwhich comprises disposing in a coniined space dense, solid granulescomprising a blowing agent and an intimate mixture of abutadiene-acrylonitrile copolymer containing at least 20% acrylonitrile,and a thermosetting phenol aldehyde resin reactive therewith, saidcopolymer and the phenol aldehyde resin being present in the ratio offrom 100 to 300 parts of the resin with 100 parts of the copolymer, saidblowing agent being within the individual solid granules, and heatingthe granules to soften them and to cause the blowing agent to evolve gaswhereby the individual granules are expanded and the surfaces of theexpanded granules are forced into contact with the surfaces of adjacentgranules and the contacting surfaces are sintered together into acontinuous network of relatively thick, substantially non-porousresinous membranes dening cells, the expanded resinous material of theinterior of the granules forming thinnermembranes subdividing said cellsinto smaller units, and continuing heating to cure the resin.

l2. A process for forming a strong, light, cellular, integral materialwhich comprises disposing in a confined space dense, solid granulescomprising a blowing agent and an intimate mixture of a resinousmaterial comprising polymerized vinyl chloride and abutadiene-acrylonitrile copolymer said mixture being characterized byflow properties such that a mass of granules of the mixture free fromblowing agent would shrink in volume and flow together when softened byheat and said blowing agent being within the individual solid granules,and heating the granules to soften them and to cause the blowing agentto evolve gas, whereby the individual granules are expanded and thesurfaces of the expanded granules of the mixture free from blowing agentadjacent granules and the contacting surfaces are sintered together intoa continuous network of relatively thick, substantially non-porousresinous membranes defining cells, the expanded resinous material of theinterior of the granules forming thinner membranes subdividing saidcells into smaller units, and continuing heating to cure the resin.

13. A process for forming a strong, light, cellular, integral materialwhich comprises disposing `in a confined space dense, solid granulescomprising a blowing agent and an intimate mixture of a resinousmaterial comprising a styrene copolymer of high styrene content and acopolymer synthetic rubber said mixture being characterized by flowproperties such that a mass of granules of the mixture free from blowingagent would shrink in Volume and ow together when softened by heat andsaid blowing agent being within the individual solid granules, andheating the granules to soften them and to cause the blowing agent toevolve gas, whereby the individual granules are expanded and thesurfaces of: the expanded granules are forced into contact with thesurfaces of adjacent granules and the contacting surfaces are sinteredtogether into a continuous network of relatively thick, substantiallynon-porous resinous membranes defining cells, the expanded resinousmaterial of the interior of the granules forming thinner membranessubdividing said cells into smaller units, and continuing heating tocure the resin.

14. A. process for forming a strong, light, cellular, integral materialwhich comprises disposing in a conned space dense, solid granulescomprising a blowing agent and an intimate mixture of a resinousmaterial comprising a styrene copolymer ci high styrene content and abutadiene styrene copolymer synthetic rubber containing 30% styrene saidmixture being characterized by flow properties such that a mass ofgranules of the mixture free from blowing agent would shrink in volumeand ilow together when softened by heat and said blowing agent beingwithin the individual solid granules, and heating the granules to softenthem and to cause the blowing agent to evolve gas, whereby theindividual granules are expanded and the surfaces of the expandedgranules are forced into contact with the surface-s of adjacent granulesand the contacting surfaces are sintered together into a continuousnetwork of relatively thick, substantially nonporous resinous membranesdefining cells, the expanded resinous material of the interior of the rgranules forming thinner membranes subdividing said cells into smallerunits, and continuing heating to cure the resin.

15. A process for forming a strong, light, cellular article whichcomprises disposing between and in contact with xed spaced surfacesdense, solid granules comprising an intimate mixture of from 100 to 30oparts by weight of a heat-softenable resin which is strong and rigid inset condition and 103 parts by weight of a synthetic polymer rubber,said blowing agent being within the individual solid granules, saidmixture of resin and synthetic rubber` being characterized by flowproperties such that a mass of granules of the mixture free from ablowing agent would shrink in volume and flow together when softened byheat, heating the granules to cause the blowing agent to expand theindividual granules to force the surfaces of the granules intocontinuous contact with the surfaces of adjacent granules and said fixedspaced surfaces, but not substantially to change the total Volumeoccupied by the granules and to soften and sinter together thecontacting surface portions of the granules into a continuous network ofrelatively thick, substantially nonporous, membranes dening cells, theexpanded material of the interior of the granules forming thinnermembranes, subdividing said cells into smaller units.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,136,096 Benner et al. Nov. 8, 1938 2,183,857 Turkington Dec.19, 1939 2,322,581 Lytle June 22, 1943 2,363,051 Dosmann Nov. 21, 19442,371,868 Berg et al. Mar. 20, 1945 2,459,739 Groton et al. Jan. 18,1949

7. A LIGHT, STRONG, INTEGRAL, CONTINUOUS CELLULAR MATERIAL COMPRISING ANETWORK OF RELATIVELY THICK SUBSTANTIALLY NONPORIYS RESINOUS MEMBRANESDEFINING CELLS AND THINNER MEMBRANES OF THE SAME COMPOSITION AS THENETWORK SUBDIVIDING SAID CELLS INTO SMALLER UNITS, SAID RESINOUSMATERIAL COMPRISING AN INTIMATE MIXTURE OF A STYRENE COPOLYMER OF HIGHSTYRENE CONTENT AND A BUTADINE-STYRENE COPOLYMER SYNTHETIC RUBBERCONTAINING 30% STYRENE.